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General reference about VMAX Host I/O Limits feature
General reference about VMAX Host I/O Limits feature
Introduction
This article indicates general reference list including FAQ, KBs, Product Guides, White papers about VMAX Host I/O Limits feature.
Detailed Information
What is VMAX Host I/O Limits?
Host I/O Limits is a feature that can be used to limit the amount of front-end (FE) bandwidth and I/Os per second (IOPs) that can be consumed by a set of Symmetrix devices over a set of director ports. This feature allows the user to place limits on the FE bandwidth and IOPs consumed by applications on the Symmetrix system. Solutions Enabler V7.5 & Requires Unisphere for VMAX V1.5 with Enginuity 5876 Service Release is required to take advantage of this feature.
How does VMAX Host I/O Limits works?
VMAX Host I/O Limits feature works on a set of devices, a Host I/O Limit is added to a storage group. A provisioning view is then created using that storage group. This causes the Host I/O Limit defined on the storage group to be applied to the devices in the storage group for the ports defined in the port group.
Host I/O Limits are defined as storage group attributes: The maximum bandwidth is displayed in MB/s (MB per second) and the maximum IOPs (I/Os per second). A Host I/O Limit can be added, removed, and modified for a storage group.
How do VMAX Host I/O limits work on cascaded storage group?
For a cascaded storage group, a Host I/O Limit can be added for either the parent or the child storage group, but not for both. If a parent storage group has a limit, the limit is shared among all its child storage groups when a provisioning view is created using the parent storage group. In addition, if a parent storage group has a limit, the user is not allowed to create provisioning views using the child storage groups.
What’s VMAX Host I/O limits Dynamic Distribution?
The dynamic distribution of Host I/O Limits can be set across configured director ports in a port group. This allows for the host I/O limit allocation on each individual port to adjuet to fluctuating demand. In the absence of dynamic distribution, each front end director in the port group is allocated a fixed value of Host I/O limits and these limits remain the same, regardless of whether other front end directors in port group are online or offline. For example, if the Host I/O Limit is 10,000 IOPS and there are two director in the port group, each director will be assigned a static (fixed) 5,000 Host I/O limit.
Solutions Enabler V7.6, Unisphere for VMAX V1.6, and Enginuity 5876 Q2 2013 Service Release and higher are required to take advantage of the new resiliency and dynamic redistribution.
How to configure VMAX Host I/O Limits?
You can use Solutions Enabler (CLI), Unisphere for VMAX (GUI) to configure VMAX Host I/O Limits feature:
To configure VMAX Host I/O Limit through Solutions Enabler, use follow command with syntax:
symsg -sid SymmID [-i Interval] [-c Count] [-v] set <[-bw_max ]>
-bw_max :Specifies the front-end maximum bandwidth in MBs/sec for the storage group. The maximum bandwidth is set to unlimited if NOLIMIT is specified.
-iops_max: Specifies the front-end maximum IOs/sec. The maximum IOs/sec is set to unlimited if NOLIMIT is specified.
The “symsg –sid SymmID set –dynamic” command is used to set the dynamic distribution of front end host I/O limits. Dynamic Distribution is disabled by default and the setting is “Never”. Dynamic distribution can be activated by changing the setting to either “OnFailure” or “Always”.
For detailed VMAX host I/O Limits configuration advice, through the Solutions Enabler command symsg, refer the latest Symmetrix Array Controls CLI Product Guide or Host I/O Limits for Symmetrix VMAX Family Arrays Technical Notes available on EMC Online Support.
To configure VMAX Host I/O Limits through Unisphere for VMAX:
1. Select a Symmetrix system.
2. Select Storage > Storage Groups to open the Storage Groupslist view.
3. Select the storage group, click more, and select Set Host I/O Limitsto open Set Host I/O Limits dialog box.
4. Select and type values for one or both of the following:
Set Host I/O Limit (MB/Sec) — Maximum bandwidth (in MB per second). Valid values range from 1 MB/sec to 100,000 MB/sec.
Set Host I/O Limit (IO/Sec) — Maximum IOPs (in I/Os per second). Valid values range from 100 IO/Sec to 100,000 IO/sec, in 100 increments.
5. To configure a dynamic distribution of host I/O limits, Set Dynamic Distribution to one of the following; otherwise, leave this field set to Never(default).
Always — Enables full dynamic distribution mode. When enabled, the configured host I/O limits will be dynamically distributed across the configured ports, thereby allowing the limits on each individual port to adjust to fluctuating demand.
Failure — Enables port failure capability. When enabled, the fraction of configured host I/O limits available to a configured port will adjust based on the number of ports currently online.
6. Click one of the following:
Add to Job List to add this task to the job list, from which you can schedule or run the task at your convenience. For more information, refer to Scheduling jobs on page 100 and Previewing/Running jobs on page 99. Expand Add to Job List, and click Run Now to perform the operation now
For detailed VMAX host I/O Limits configuration advice, through Unisphere for VMAX, refer the latest Unisphere for VMAX product guide available on EMC Online Support.
VMAX Host I/O Limits Known Issue & Knowledge Bases:
Why is the Host I/O limit feature in Solutions Enabler allowing I/O to exceed the set limit?
How do I set Host I/O Limits through Solutions Enabler?
VMAX Host I/O Limits White Papers:
White Paper: Application workload control using Host I/O Limits for SQL Server on EMC Symmetrix VMAX
Author: Fenglin Li
iEMC APJ
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